I recently launched a paysite network of (3) exclusive sites... so, I may be able to save you some time and effort with a quick bit about my experiences using CCBill and NATS so far.
I started out using CCBill straight up. No problems at all. They are easy people to work with, completely trustworthy and have a helpful support team. However, you will quickly find that the back-end of CCBill is cumbersome and inexplicably poorly designed (I have no idea why they have not updated it from a usability standpoint). If you have ever used the affiliate side of the CCBill back-end you know what to expect as a client. Links that are far less than intuitive, millions of 'extra clicks' that should not be needed, slow lackluster and overly complicated software overall. That being said, many webmasters are used to CCBill and trust CCBill - as do many surfers. There are many webmasters who have told me point blank that they will not promote a program unless they know you personally or know they are being paid by a trusted third party like CCBill. So unless you have affiliates already sending you traffic without CCBill... plan on using CCBill to start no matter what.
On the other hand, you will also find that many other affiliates won't promote a CCBill program and demand NATS or MPA or their favorite flavor of the month stats system because NATS has far superior stats and tracking capabilities for program owners and affiliates alike. The software is infinitely better and things that take 10 minutes to do in CCBill take 10 clicks to do in NATS. That being said, the support from NATS is far weaker than the support from CCBill. One answers your calls on the third ring 24/7 and walks you through whatever you need... the other expects emailed trouble tickets and they get back to you when they get back to you. Most webmasters who like NATS have told me they prefer NATS 3.0 not NATS 4.0 because while 4.0 added a ton of new tools it also became far less simple to use. NATS 3 has a simple, elegantly designed report page that NATS 4 inexplicably fails to offer. I have been told by the owner of NATS that they will soon be releasing a 'simple theme' for NATS 4 that will emulate the simplicity of NATS 3, but I have not been given any ETA on when that will be released.
Right now I am planning on either running NATS 4 with the payments being generated directly by CCBill as a hybrid of the best of both, or planning to run both side by side with my affiliates able to choose one or the other depending on which they prefer. Keep in mind, this doesn't even begin to take into account cascading billing or alternate payment processors.
As an overhead cost, the smallest program package offered by NATS runs $150 a month, and CCBill charges 14.5% to the smallest programs it handles. So running NATS through CCBill or side by side will cost you $150 + 14.5% of each sale per month to start out. That means if you charge $20-30 per month for each sale and don't offer trials, you would need about 6-8 sales/rebills a month just to cover the cost of your stats and processing. That doesn't include the $750 fee to accept visa, the few hundred bucks a month you can expect for hosting, the cost of content and updates, the payouts to any affiliates who do send you traffic and so on.... Plan on spending thousands not hundreds if you decide to launch some sites. The people who plan on spending hundreds are out of business before they even get a chance to be in business.
Feel free to contact me on ICQ# 266942896 if you do launch some sites, there are several ways I can help you, including sending high quality affiliate traffic and helping you to use the review site submitter on webmasterscore.com to send your sites out for review by 60+ review sites.
